When talking about the German Kriegsmarine in World War II, the German U-Boats are often the first thing that comes into mind. At the outbreak of the war of the war, Germany had 57 U-Boats, most of them not capable of operations in the Atlantic. It was planned to build about 250 in the Naval construction program called Z-Plan, but since this plan was never realized, Germany entered the war with a much less number of submarines than the allied nations. In following 6 years, over 1100 boats were built, and was often seen as the biggest threat to Great Britain in the whole war.
Those submarines operated in all oceans of the world - from the North Sea, to the Atlantic, the American Coast (Operation Donnerschlag), the Arctic and even the Indian Ocean and the Pacific - until mid 1943 they were superior to their allied hunters. But with the introduction of radar, Huff Duff, and a continuous air cover for allied convoys, the former hunter got the hunted, even the introduction of new, revolutionary Submarines like the Type XXI could not change this.
Besides their success in the early years of the war, the U-Boats paid a terrible price for it. About 80% of all U-Boats were destroyed, 28.000 of the 40.000 U-boat personal were killed during the war, 8.000 were captured.
Since detailed information for all U-Boat classes and single ships would be too voluminous for this web page, only a short overview about the single U-Boat types is given here.